基于合金介电常数的可控特性增强光子自旋霍尔效应

基于平面角谱理论,系统研究了BK7玻璃-合金薄膜-空气结构中合金介电常数的变化对反射光自旋霍尔效应的调控规律.数值仿真结果表明,该结构发生表面等离激元共振的共振角主要受合金介电常数实部的影响,随介电常数实部的增加而增大,而虚部对共振角变化的影响相对较小.不同介电常数合金在其共振角处得到的较大光子自旋霍尔效应横移呈集中的带状分布,选取介电常数-2.8+1.6i的Ag-Ni合金时,光子自旋霍尔效应横移能达到1.2×10~5 nm.研究还发现将入射角固定为44.1°时,光子自旋霍尔效应横移随合金介电常数的变化呈轴对称分布,并以最大值为中心呈球面状辐射,离中心点越远光子自旋霍尔效应横移越小.选取介电常数-10.6+1.2i的Ag-Au合金时,光子自旋霍尔效应横移最大能达到8000 nm,相比于以往纯金属纳米结构BK7玻璃-金-空气中得到的最大光子自旋霍尔效应横移3000 nm有了较大的提高.该研究不仅能够有效增强光子自旋霍尔效应,还能为设计等离激元共振传感器等纳米光子器件提供理论依据.     

Switching the direction of spin accumulation in the spin Hall effect of light by adjusting the optical axis of an uniaxial crystal

We theoretically and experimentally investigate a switchable spin Hall effect (SHE) of light in reflection near the Brewster angle at an air-uniaxial crystal interface. We find a large transverse spin splitting near the Brewster angle, whose sign can be altered by rotating the optical axis. As an analogy of the SHE in an electronic system, a switchable spin accumulation in the SHE of light is detected. We are able to switch the direction of the spin accumulation by adjusting the optical axis angle of the uniaxial crystal. These findings may give opportunities for photon spin manipulating and developing a new generation of nano-photonic devices.     

Photonic spin Hall effect in PT symmetric metamaterials

We proposed and demonstrated that PT symmetric metamaterials could be used to achieve enhanced spin Hall effect (SHE) of light. We find that when laser mode is excited in PT symmetric system, the enhanced SHE could be obtained in both transmitted and reflected beams. In addition, as exceptional points (EPs) of PT symmetric system can happen for both p- and s-polarizations, the enhanced SHE of reflected light can function for both horizontally and vertically polarized incident beams. Particularly, these EPs can lead to unidirectional reflectionlessness, asymmetric SHE with maximum contrast ratio of 48 is obtained by launching light beams near EPs. Our work opens up a new path to obtain enhanced transverse displacement for both reflected and transmitted light and enables more opportunities in manipulating photonic SHE.     

均匀等离子体光栅的色散特性研究

最近研究表明,两束交叉激光脉冲在等离子体中传播时,可以诱导生成周期等离子体密度调制(或称等离子体布拉格光栅). 分别利用传输矩阵法和耦合模理论,推导了激光斜入射时等离子体光栅的色散关系. 两种方法均表明,均匀等离子体光栅存在着光子带隙结构,并且在带隙附近有强烈的色散. 当激光斜入射时,带隙结构会呈现不同的偏振特性：S偏振光的带隙宽度随着入射角的增大而逐渐变宽,而P偏振光的带隙宽度随着入射角的增大先迅速变窄,在布儒斯特角入射时带隙消失,然后又随着入射角的增大而迅速变宽. 超宽的光子带隙和超高的激光损伤阈值,使得等离子体光栅有望成为一种新型的操纵强激光脉冲的光子器件. 关键词： 等离子体光栅 传输矩阵法 耦合模理论 光子带隙     

Mixed Fano-SP resonant absorption of THz electromagnetic waves in a photonic resonator contacting with a metal film

In terahertz frequency region, we have investigated theoretically the correlation between spectra of a free photonic structure and that deposited on a metal for several models of metal. It was found that for quasi-normal incidence of p-polarized electromagnetic field the presence of metal generates narrow spectral wells in the middle of reflection windows existing in a free photonic crystal. Quite another manifestation of metal-resonator inter-influence takes place at incident angles exceeding the Brewster angle when reflection spikes coincide with modes of photonic crystal resonator and they are absent throughout the stopband areas. The effects are strongly depended on polarization, number of periods and angle of incidence.     

Photonic spin Hall effect and terahertz gas sensor via InSb-supported long-range surface plasmon resonance

We propose a simple one-dimensional grating coupling system that can excite multiple surface plasmon resonances for refractive index(RI)sensing with self-reference characteristics in the near-infrared band.Using theoretical analysis and the finite-difference time-domain method,the plasmonic mechanism of the structure is discussed in detail.The results show that the excited resonances are independent of each other and have different fields of action.The mode involving extensive interaction with the analyte environment achieves a high sensitivity of 1236 nm/RIU,and the figure of merit(FOM)can reach 145 RIU-1.Importantly,the mode that is insensitive to the analyte environment exhibits good self-reference characteristics.Moreover,we discuss the case of exchanging the substrate material with the analyte environment.Promising simulation results show that this RI sensor can be widely deployed in unstable and complicated environments.     

Spin Hall effect of a light beam in anisotropic metamaterials

<正>We theoretically investigate a switchable spin Hall effect of light(SHEL) in reflection for three specific dispersion relations at an air-anisotropic metamaterial interface.The displacements of horizontal and vertical polarization components vary with the incident angle at different dispersion relations.The transverse displacements can be obtained with the relevant metamaterial whose refractive index can be arbitrarily tailed.The results of the SHEL in the metarnaterial provide a new way for manipulating the transverse displacements of a specific polarization component.     

Investigation of Brewster anomalies in one-dimensional disordered media having Lévy-type distribution

In this paper, we calculate the localization length of a TM electromagnetic wave in unitof system length versus incident angle in a disordered layered structure where therefractive index of one of its constituents follows a Lévy-type distribution with a powerexponent α.The incident angle at which the localization length takes the maximum value is called thegeneralized Brewster angle as before. However, in contrast to previous works with a weakdisorder, the wave incident at generalized Brewster angle is not always in the extendedregime. For special values of α and the frequency, the system is in a localizedstate at this angle. But, the localization length at this Brewster angle is always largerthan that at other angles. The effects of α variation on the localization length at thisBrewster angle and its position are investigated for different frequencies. Thelocalization at this angle degrades with increasing α for all frequencies. Atsome working frequencies, the generalized Brewster angle is a decreasing function ofα. However,at other frequencies, the dependence of generalized Brewster angle on α is not monotonic. Forincident angles smaller than a specific angle, the localization length increases withincreasing α.However, for incident angles larger than this specific angle, there are incident angles atwhich any increase of α leads to the decrease of localization length. Inother words, for these incident angles, the improvement of Anderson localizationsurprisingly happens with decrease of disorder strength and the refractive index contrast.     

Large negative Goos-Hanchen shift at metal surfaces

It has been previously established that for p-polarized light incident onto a semi-infinite absorbing medium, large negative Goos-Hanchen (GH) shifts can be expected in the case of weak absorption at incidence close to the Brewster angle. The effect has been demonstrated for certain semiconducting media at optical frequencies. Here we point out that similar phenomenon can take place for strongly reflecting and attenuating medium such as metal at IR frequencies, with large incident angles close to grazing incidence. Moreover, unlike the previously-studied case with semiconductors, the Brewster angle in the present case with metals plays an insignificant role in the possible hindrance of the observation of such large negative shifts.     

Photonic Spin Hall Effect as a Highly Sensitive Refractive Index Sensing Platform for Glucose

This study presents an innovative refractive index (RI) sensor that measures glucose concentration by utilizing the photonic spin Hall effect (SHE) in a resonant optical tunneling effect (ROTE) structure. The ROTE structure consists of three InP layers with the high RI and two analyte layers (with a high-low-high-low-high RI distribution), in which glucose solution samples with the low RI are injected. By subjecting the InP layers to external bias-assisted light, the photonic SHE can be flexibly manipulated, enabling the modulation of the sensing performance accordingly. It is found that the transverse shift of photonic SHE presents a large variation in response to the tiny change in glucose concentrations. By optimizing the parameters (i.e., intensity or wavelength) of bias light, the sensitivity of this sensor can reach as high as 735.7 µm RIU⁻¹. Compared to traditional glucose sensors, this original work implements the novel photonic SHE with the superior sensing performance. Therefore, the proposed design shows promising potential for biomedical applications, such as medical diagnoses and drug discovery.     

Study on modulation of near infrared radiation based on plasma photonic crystal

In this paper, a plasma photonic crystal (PPC) for infrared radiation modulation which is composed of indium tin oxide (ITO) and plasma is proposed. The performance of plasma photonic crystal in near infrared radiation modulation is researched by transfer matrix method (TMM). The simulation results show that the near infrared radiation pass band can be adjusted by the changing of plasma frequency of plasma. The reflection to near infrared radiation by plasma photonic crystal increases with plasma frequency and that of absorption decreases. In addition, the modulation performance of the plasma photonic crystal at different incidence wave angles is also studied. The results show that the incident wave angles have little effect on the transmission of plasma photonic crystal in near infrared band. The reflection of the plasma photonic crystal to near infrared radiation decreases with increasing of the incident wave angle, but that of the absorption increases with the incident wave angle. Therefore, the proposed plasma photonic crystal has a potential application in tunable near infrared filter devices.     

折射率梯度引起反转的光自旋霍尔效应研究

从经典电动力学出发,研究了由折射率梯度导致的反转光自旋霍尔效应。通过分析光从光疏介质入射到光密介质和从光密介质入射到光疏介质两种情况,揭示了光自旋霍尔效应中的横移与偏振态、折射率梯度以及入射角等因素的定性关系。当入射角一定时,光从光疏介质入射到光密介质时的水平偏振横移绝对值大于垂直偏振横移,而从光密介质入射到光疏介质的情况正好与之相反,并且传输场的横移方向取决于折射率梯度方向,增大入射角能明显增强光自旋霍尔效应,对某一特定的线偏振光束,其左、右旋圆偏振光分量的横移等值反向。这些研究结果为调控光自旋霍尔效应提供了有效途径。     

A Janus Logic Gate with Sensing Function

A layered metastructure (LM) formed by a quasi-periodic arrangement of graphene and isotropic dielectric mediums, which can realize the functions of the tunable logic gate and refractive index (RI) sensing based on spin Hall effect (SHE), is theoretically studied. The asymmetric arrangement of the mediums and the increased angle of the incident electromagnetic waves (EWs) equip the LM with Janus feature. Through the modulation of the graphene chemical potential, the sharp absorption peak (AP) in the terahertz (THz) range can be obtained, and then the AP can be used to implement NOT logic and OR logic respectively corresponding to the forward and backward scales. By locating the incident angle of light corresponding to the SHE displacement peak, the linear measurement relationship between RI and SHE angle can be realized, and the widest RI measurement range is 1–1.4 with the angles changing from 21.88° to 61.84°. Additionally, a good linear range can be achieved, owning the optimum sensitivity (S) up to 153.5° RIU⁻¹. The RI sensing still strictly follows the logic functions of the forward NOT and backward OR via adjusting the chemical potential of graphene and discriminating the peak value of SHE displacement.     

Design of an omnidirectional band gap independent of ambient media refractive indices by using a heterostructure magnetic photonic crystal

This paper aims to study the general conditions under which omnidirectional band gaps (OBGs) are achieved by using heterostructure magnetic photonic crystals (HMPCs). These structures contain periodic layers with alternative dielectric permittivity and magnetic permeability. The proposed design offers the stacking of two magnetic photonic crystals (MPCs), where one MPC has Brewster’s angle at TE polarization and another has the angle at TM polarization. The propagation of electromagnetic waves is investigated by means of the transfer matrix method. Also, the total reflection frequency range for any incident angle and polarization is discussed in this paper. As a conclusion, although each MPC has no OBG individually, the proposed HMPC may contain an OBG. The main advantage of the proposed design is that the obtained OBG is independent of the ambient media refractive index. Therefore, it can be used in engineering omnireflectors in integrated photonics.     

A Promising Mechanism for Photonic Spin Hall Effect and Refractive Index Sensing: Surface Exciton Polaritons

Surface polaritons are surface electromagnetic waves propagating along the surface of a medium, which play an important role in enhancing the photonic spin Hall effect (SHE). Among them, the successful excitation of surface exciton polaritons (SEPs) often requires cryogenic temperature, which limits their practical applications. In this contribution, a promising mechanism is presented for enhancing the photonic SHE by taking advantage of room-temperature SEPs in a prism-glass-TDBC-air configuration. By depositing the TDBC layer on plasmon active metal, the hybrid polariton, namely, surface plasmon exciton polariton (SPEP) can be observed, which gives rise to the further enhancement of photonic SHE. Furthermore, a refractive index sensor based on SEP (or SPEP) enhanced photonic SHE is proposed with the superior sensing performance. The results pave the way for the realization of giant photonic SHE in this simple and promising method, and offer the opportunity for developing highly sensitive optical sensors.     

Influence of the polarization and optical axis on the transmission behavior in a one dimensional photonic crystal containing uniaxial metamaterial

In this letter, we introduce a one-dimensional photonic crystal (1DPC) structure with a uniaxial metamaterial defect layer. It is proposed to control the transmitted wave of the defect mode by adjusting the orientation of the optical axis and incidence angle for both polarization states. The 4 × 4 transfer matrix method was employed to calculate the transmittance spectrum of the proposed structure. It is shown that the photonic band gaps, the intensity and the peak wavelength of the defect mode depends on the polarization, the orientation of the optical axis and the incidence angle of the wave, due to the strong anisotropy of the metamaterial. The transmittance spectrum curves at different optical axes of the uniaxial metamaterial and the distinct incidence angles are illustrated graphically. It is shown that the defect mode appears as a peak in the transmission spectrum. Pronounced contrasts in the intensity, wavelength positions of the defect mode and photonic band gap were demonstrated depending on the incidence angle and the orientation of the optical axis of the uniaxial metamaterial defect layer for both polarizations. Our structure offers a great variety of possibilities for designing and controlling the transmitted intensity of the defect mode.     

Scattering of an electromagnetic wave from a slightly random dielectric surface: Yoneda peak and Brewster angle in incoherent scattering

Abstract

The scattering of an electromagnetic wave from a two-dimensional, slightly rough dielectric surface is studied based on the stochastic functional approach. It is shown that in the case of TM(p)-polarized incidence there exists a zero in the incoherent scattering at the angle we call the ‘Brewster scattering angle’, which depends on the incident angle in contrast to the Brewster angle of coherent reflection which is independent of the incident angle, that a ‘quasi-anomalous scattering’ can generally occur in the optically denser medium at the critical angle of total reflection in both TE(s)- and TM(p)-polarized incidence, regardless of which side of the random surface is illuminated, and that the Yoneda peak in the x-ray scattering can be interpreted as a special case of the quasi-anomalous scattering which becomes sharper when the relative refractive index becomes closer to unity as in the x-ray region. Cross-polarized scattering and enhanced backscattering due to the second-order effect are also calculated.     

光自旋霍尔效应中的交叉偏振特性研究

从光束角谱理论出发建立了描述光自旋霍尔效应的傍轴传输模型, 利用这一模型分析了光自旋霍尔效应中的交叉偏振特性. 通过分析交叉偏振效应强度和入射角变化的规律, 发现交叉偏振效应越强, 光自旋霍尔效应中的自旋分裂越大. 为便于实验观察, 将入射角选在光自旋霍尔效应较强的布儒斯特角附近, 观测到了强的交叉偏振效应. 增大交叉偏振分量的同时减小初始偏振分量, 可显著增强光自旋霍尔效应. 这一调控方法为研制基于光自旋霍尔效应的新型光子器件提供了理论基础.     

转换反射中光自旋霍尔效应的自旋堆积方向

从理论上和实验上研究了转换反射中光自旋霍尔效应的自旋堆积方向的方法,建立了描述光束在空气-棱镜界面反射的自旋堆积模型,揭示了横移与光束入射偏振角的定性关系。研究发现,当入射角小于布儒斯特角时,随着入射偏振角的逐渐增大,自旋堆积的方向发生反转。而当入射角大于布儒斯特角时,自旋堆积的方向不再随入射偏振角的变化而反转。结果表明,在光束入射角为确定值且小于布儒斯特角的情况下,可以通过调控光束的入射偏振角转换自旋堆积的方向。转换自旋堆积方向的研究为有效调控光自旋霍尔效应提供了新的途径。     

Magnetorefractive effect in nanocomposites: Dependence on the angle of incidence and on light polarization

The polarization and angular dependences of the magnetorefractive effect (MRE) in metal-insulator nanocomposites in reflection and transmission geometries have been calculated in terms of the high-frequency, spin-dependent tunneling mechanism. The MRE exhibits a weak polarization and angular response at small angles of incidence. The MRE in reflection and transmission starts to grow strongly with increasing angle of incidence. The MRE in reflection in nanocomposites with metal contents corresponding to the insulating phase near the percolation threshold reaches the largest values with p-polarized light at an angle of incidence close to the Brewster angle. The results of the calculation are in a qualitative agreement with experimental data.